1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2018-2019 SiFive, Inc.
4 * Wesley Terpstra
5 * Paul Walmsley
6 *
7 * This library supports configuration parsing and reprogramming of
8 * the CLN28HPC variant of the Analog Bits Wide Range PLL. The
9 * intention is for this library to be reusable for any device that
10 * integrates this PLL; thus the register structure and programming
11 * details are expected to be provided by a separate IP block driver.
12 *
13 * The bulk of this code is primarily useful for clock configurations
14 * that must operate at arbitrary rates, as opposed to clock configurations
15 * that are restricted by software or manufacturer guidance to a small,
16 * pre-determined set of performance points.
17 *
18 * References:
19 * - Analog Bits "Wide Range PLL Datasheet", version 2015.10.01
20 * - SiFive FU540-C000 Manual v1p0, Chapter 7 "Clocking and Reset"
21 * https://static.dev.sifive.com/FU540-C000-v1.0.pdf
22 */
23
24 #include <linux/bug.h>
25 #include <linux/err.h>
26 #include <linux/limits.h>
27 #include <linux/log2.h>
28 #include <linux/math64.h>
29 #include <linux/math.h>
30 #include <linux/minmax.h>
31
32 #include <linux/clk/analogbits-wrpll-cln28hpc.h>
33
34 /* MIN_INPUT_FREQ: minimum input clock frequency, in Hz (Fref_min) */
35 #define MIN_INPUT_FREQ 7000000
36
37 /* MAX_INPUT_FREQ: maximum input clock frequency, in Hz (Fref_max) */
38 #define MAX_INPUT_FREQ 600000000
39
40 /* MIN_POST_DIVIDE_REF_FREQ: minimum post-divider reference frequency, in Hz */
41 #define MIN_POST_DIVR_FREQ 7000000
42
43 /* MAX_POST_DIVIDE_REF_FREQ: maximum post-divider reference frequency, in Hz */
44 #define MAX_POST_DIVR_FREQ 200000000
45
46 /* MIN_VCO_FREQ: minimum VCO frequency, in Hz (Fvco_min) */
47 #define MIN_VCO_FREQ 2400000000UL
48
49 /* MAX_VCO_FREQ: maximum VCO frequency, in Hz (Fvco_max) */
50 #define MAX_VCO_FREQ 4800000000ULL
51
52 /* MAX_DIVQ_DIVISOR: maximum output divisor. Selected by DIVQ = 6 */
53 #define MAX_DIVQ_DIVISOR 64
54
55 /* MAX_DIVR_DIVISOR: maximum reference divisor. Selected by DIVR = 63 */
56 #define MAX_DIVR_DIVISOR 64
57
58 /* MAX_LOCK_US: maximum PLL lock time, in microseconds (tLOCK_max) */
59 #define MAX_LOCK_US 70
60
61 /*
62 * ROUND_SHIFT: number of bits to shift to avoid precision loss in the rounding
63 * algorithm
64 */
65 #define ROUND_SHIFT 20
66
67 /*
68 * Private functions
69 */
70
71 /**
72 * __wrpll_calc_filter_range() - determine PLL loop filter bandwidth
73 * @post_divr_freq: input clock rate after the R divider
74 *
75 * Select the value to be presented to the PLL RANGE input signals, based
76 * on the input clock frequency after the post-R-divider @post_divr_freq.
77 * This code follows the recommendations in the PLL datasheet for filter
78 * range selection.
79 *
80 * Return: The RANGE value to be presented to the PLL configuration inputs,
81 * or a negative return code upon error.
82 */
__wrpll_calc_filter_range(unsigned long post_divr_freq)83 static int __wrpll_calc_filter_range(unsigned long post_divr_freq)
84 {
85 if (post_divr_freq < MIN_POST_DIVR_FREQ ||
86 post_divr_freq > MAX_POST_DIVR_FREQ) {
87 WARN(1, "%s: post-divider reference freq out of range: %lu",
88 __func__, post_divr_freq);
89 return -ERANGE;
90 }
91
92 switch (post_divr_freq) {
93 case 0 ... 10999999:
94 return 1;
95 case 11000000 ... 17999999:
96 return 2;
97 case 18000000 ... 29999999:
98 return 3;
99 case 30000000 ... 49999999:
100 return 4;
101 case 50000000 ... 79999999:
102 return 5;
103 case 80000000 ... 129999999:
104 return 6;
105 }
106
107 return 7;
108 }
109
110 /**
111 * __wrpll_calc_fbdiv() - return feedback fixed divide value
112 * @c: ptr to a struct wrpll_cfg record to read from
113 *
114 * The internal feedback path includes a fixed by-two divider; the
115 * external feedback path does not. Return the appropriate divider
116 * value (2 or 1) depending on whether internal or external feedback
117 * is enabled. This code doesn't test for invalid configurations
118 * (e.g. both or neither of WRPLL_FLAGS_*_FEEDBACK are set); it relies
119 * on the caller to do so.
120 *
121 * Context: Any context. Caller must protect the memory pointed to by
122 * @c from simultaneous modification.
123 *
124 * Return: 2 if internal feedback is enabled or 1 if external feedback
125 * is enabled.
126 */
__wrpll_calc_fbdiv(const struct wrpll_cfg * c)127 static u8 __wrpll_calc_fbdiv(const struct wrpll_cfg *c)
128 {
129 return (c->flags & WRPLL_FLAGS_INT_FEEDBACK_MASK) ? 2 : 1;
130 }
131
132 /**
133 * __wrpll_calc_divq() - determine DIVQ based on target PLL output clock rate
134 * @target_rate: target PLL output clock rate
135 * @vco_rate: pointer to a u64 to store the computed VCO rate into
136 *
137 * Determine a reasonable value for the PLL Q post-divider, based on the
138 * target output rate @target_rate for the PLL. Along with returning the
139 * computed Q divider value as the return value, this function stores the
140 * desired target VCO rate into the variable pointed to by @vco_rate.
141 *
142 * Context: Any context. Caller must protect the memory pointed to by
143 * @vco_rate from simultaneous access or modification.
144 *
145 * Return: a positive integer DIVQ value to be programmed into the hardware
146 * upon success, or 0 upon error (since 0 is an invalid DIVQ value)
147 */
__wrpll_calc_divq(u32 target_rate,u64 * vco_rate)148 static u8 __wrpll_calc_divq(u32 target_rate, u64 *vco_rate)
149 {
150 u64 s;
151 u8 divq = 0;
152
153 if (!vco_rate) {
154 WARN_ON(1);
155 goto wcd_out;
156 }
157
158 s = div_u64(MAX_VCO_FREQ, target_rate);
159 if (s <= 1) {
160 divq = 1;
161 *vco_rate = MAX_VCO_FREQ;
162 } else if (s > MAX_DIVQ_DIVISOR) {
163 divq = ilog2(MAX_DIVQ_DIVISOR);
164 *vco_rate = MIN_VCO_FREQ;
165 } else {
166 divq = ilog2(s);
167 *vco_rate = (u64)target_rate << divq;
168 }
169
170 wcd_out:
171 return divq;
172 }
173
174 /**
175 * __wrpll_update_parent_rate() - update PLL data when parent rate changes
176 * @c: ptr to a struct wrpll_cfg record to write PLL data to
177 * @parent_rate: PLL input refclk rate (pre-R-divider)
178 *
179 * Pre-compute some data used by the PLL configuration algorithm when
180 * the PLL's reference clock rate changes. The intention is to avoid
181 * computation when the parent rate remains constant - expected to be
182 * the common case.
183 *
184 * Returns: 0 upon success or -ERANGE if the reference clock rate is
185 * out of range.
186 */
__wrpll_update_parent_rate(struct wrpll_cfg * c,unsigned long parent_rate)187 static int __wrpll_update_parent_rate(struct wrpll_cfg *c,
188 unsigned long parent_rate)
189 {
190 u8 max_r_for_parent;
191
192 if (parent_rate > MAX_INPUT_FREQ || parent_rate < MIN_POST_DIVR_FREQ)
193 return -ERANGE;
194
195 c->parent_rate = parent_rate;
196 max_r_for_parent = div_u64(parent_rate, MIN_POST_DIVR_FREQ);
197 c->max_r = min_t(u8, MAX_DIVR_DIVISOR, max_r_for_parent);
198
199 c->init_r = DIV_ROUND_UP_ULL(parent_rate, MAX_POST_DIVR_FREQ);
200
201 return 0;
202 }
203
204 /**
205 * wrpll_configure_for_rate() - compute PLL configuration for a target rate
206 * @c: ptr to a struct wrpll_cfg record to write into
207 * @target_rate: target PLL output clock rate (post-Q-divider)
208 * @parent_rate: PLL input refclk rate (pre-R-divider)
209 *
210 * Compute the appropriate PLL signal configuration values and store
211 * in PLL context @c. PLL reprogramming is not glitchless, so the
212 * caller should switch any downstream logic to a different clock
213 * source or clock-gate it before presenting these values to the PLL
214 * configuration signals.
215 *
216 * The caller must pass this function a pre-initialized struct
217 * wrpll_cfg record: either initialized to zero (with the
218 * exception of the .name and .flags fields) or read from the PLL.
219 *
220 * Context: Any context. Caller must protect the memory pointed to by @c
221 * from simultaneous access or modification.
222 *
223 * Return: 0 upon success; anything else upon failure.
224 */
wrpll_configure_for_rate(struct wrpll_cfg * c,u32 target_rate,unsigned long parent_rate)225 int wrpll_configure_for_rate(struct wrpll_cfg *c, u32 target_rate,
226 unsigned long parent_rate)
227 {
228 unsigned long ratio;
229 u64 target_vco_rate, delta, best_delta, f_pre_div, vco, vco_pre;
230 u32 best_f, f, post_divr_freq;
231 u8 fbdiv, divq, best_r, r;
232 int range;
233
234 if (c->flags == 0) {
235 WARN(1, "%s called with uninitialized PLL config", __func__);
236 return -EINVAL;
237 }
238
239 /* Initialize rounding data if it hasn't been initialized already */
240 if (parent_rate != c->parent_rate) {
241 if (__wrpll_update_parent_rate(c, parent_rate)) {
242 pr_err("%s: PLL input rate is out of range\n",
243 __func__);
244 return -ERANGE;
245 }
246 }
247
248 c->flags &= ~WRPLL_FLAGS_RESET_MASK;
249
250 /* Put the PLL into bypass if the user requests the parent clock rate */
251 if (target_rate == parent_rate) {
252 c->flags |= WRPLL_FLAGS_BYPASS_MASK;
253 return 0;
254 }
255
256 c->flags &= ~WRPLL_FLAGS_BYPASS_MASK;
257
258 /* Calculate the Q shift and target VCO rate */
259 divq = __wrpll_calc_divq(target_rate, &target_vco_rate);
260 if (!divq)
261 return -1;
262 c->divq = divq;
263
264 /* Precalculate the pre-Q divider target ratio */
265 ratio = div64_u64((target_vco_rate << ROUND_SHIFT), parent_rate);
266
267 fbdiv = __wrpll_calc_fbdiv(c);
268 best_r = 0;
269 best_f = 0;
270 best_delta = MAX_VCO_FREQ;
271
272 /*
273 * Consider all values for R which land within
274 * [MIN_POST_DIVR_FREQ, MAX_POST_DIVR_FREQ]; prefer smaller R
275 */
276 for (r = c->init_r; r <= c->max_r; ++r) {
277 f_pre_div = ratio * r;
278 f = (f_pre_div + (1 << ROUND_SHIFT)) >> ROUND_SHIFT;
279 f >>= (fbdiv - 1);
280
281 post_divr_freq = div_u64(parent_rate, r);
282 vco_pre = fbdiv * post_divr_freq;
283 vco = vco_pre * f;
284
285 /* Ensure rounding didn't take us out of range */
286 if (vco > target_vco_rate) {
287 --f;
288 vco = vco_pre * f;
289 } else if (vco < MIN_VCO_FREQ) {
290 ++f;
291 vco = vco_pre * f;
292 }
293
294 delta = abs(target_rate - vco);
295 if (delta < best_delta) {
296 best_delta = delta;
297 best_r = r;
298 best_f = f;
299 }
300 }
301
302 c->divr = best_r - 1;
303 c->divf = best_f - 1;
304
305 post_divr_freq = div_u64(parent_rate, best_r);
306
307 /* Pick the best PLL jitter filter */
308 range = __wrpll_calc_filter_range(post_divr_freq);
309 if (range < 0)
310 return range;
311 c->range = range;
312
313 return 0;
314 }
315
316 /**
317 * wrpll_calc_output_rate() - calculate the PLL's target output rate
318 * @c: ptr to a struct wrpll_cfg record to read from
319 * @parent_rate: PLL refclk rate
320 *
321 * Given a pointer to the PLL's current input configuration @c and the
322 * PLL's input reference clock rate @parent_rate (before the R
323 * pre-divider), calculate the PLL's output clock rate (after the Q
324 * post-divider).
325 *
326 * Context: Any context. Caller must protect the memory pointed to by @c
327 * from simultaneous modification.
328 *
329 * Return: the PLL's output clock rate, in Hz. The return value from
330 * this function is intended to be convenient to pass directly
331 * to the Linux clock framework; thus there is no explicit
332 * error return value.
333 */
wrpll_calc_output_rate(const struct wrpll_cfg * c,unsigned long parent_rate)334 unsigned long wrpll_calc_output_rate(const struct wrpll_cfg *c,
335 unsigned long parent_rate)
336 {
337 u8 fbdiv;
338 u64 n;
339
340 if (c->flags & WRPLL_FLAGS_EXT_FEEDBACK_MASK) {
341 WARN(1, "external feedback mode not yet supported");
342 return ULONG_MAX;
343 }
344
345 fbdiv = __wrpll_calc_fbdiv(c);
346 n = parent_rate * fbdiv * (c->divf + 1);
347 n = div_u64(n, c->divr + 1);
348 n >>= c->divq;
349
350 return n;
351 }
352
353 /**
354 * wrpll_calc_max_lock_us() - return the time for the PLL to lock
355 * @c: ptr to a struct wrpll_cfg record to read from
356 *
357 * Return the minimum amount of time (in microseconds) that the caller
358 * must wait after reprogramming the PLL to ensure that it is locked
359 * to the input frequency and stable. This is likely to depend on the DIVR
360 * value; this is under discussion with the manufacturer.
361 *
362 * Return: the minimum amount of time the caller must wait for the PLL
363 * to lock (in microseconds)
364 */
wrpll_calc_max_lock_us(const struct wrpll_cfg * c)365 unsigned int wrpll_calc_max_lock_us(const struct wrpll_cfg *c)
366 {
367 return MAX_LOCK_US;
368 }
369